Analyzer solves spiking readings

Problem

Chlorine and water were not mixing thoroughly at a drinking water plant in South Carolina, producing incomplete conversions to monochloramine that affected residual life and disinfection byproduct formation. Monitoring revealed the issue.

 

Solution

The facility installed a CLT10 sc total chlorine reagentless amperometric analyzer from Hach next to a diethyl phenylene diamine (DPD) colorimetric instrument. Data from the amperometric unit showed trending of the colorimetric analyzer and shed light on multiple spikes not visible in other tests. Continuous data from the instrument showed that instability of pH and chlorine concentration values were causing the spikes.

The team knew pH instability alone should not have caused the spiking chlorine readings due to the pH compensation option on the instrument. They hypothesized that spiking was due to incomplete mixing and reaction of free chlorine and ammonia. Their theory was proven when the analyzer was moved farther away from the original sampling point and the spikes disappeared.

 

Result:

The plant was better able to control dosing. Using online monitoring, operators pinpointed the unexpected problem with mixing disinfection chemicals in the drinking water. 800/227-4224; www.hach.com.

 

Flowmeter eliminates signal damping

Problem

Microbubbles in the two-stage nanofiltration system of a southeast Florida water utility made flow measurement and pressure control difficult. Erratic and noisy signals from pulsed DC electromagnetic flowmeters degraded accuracy and upset the SCADA system.

 

Solution

As a trial, the utility installed an FSM4000 electromagnetic flowmeter from ABB on a nanofiltration train. The unit, combining AC and DC excitation of the magnetic field, operates at 70 Hz. The high frequency eliminates the need for output signal damping in noisy applications. Advanced digital filtering allows the extraction of smooth, accurate flow rate values from noisy sensor signals.

 

Result:

The trial was successful. The utility plans to install meters on the other four trains in the system. 800/829-6001; www.abb.com.